The Moncada Formation in western Cuba is an ∼2-m-thick weakly metamorphosed complex characterized by repetition of calcareous sandstone units that show overall upward fining and thinning. The Moncada Formation contains abundant shocked quartz, altered vesicular impact-melt fragments, and altered and deformed greenish grains of possible impact glass origin. In addition, a high iridium (∼0.8 ppb) peak is identified at the top of the formation. Together with the biostratigraphically estimated age, between late Maastrichtian and early Paleocene, this evidence supports a Cretaceous-Tertiary (K-T) boundary origin for the deposit. The Moncada Formation has ripple cross-laminations at several horizons that indicate north-south-trending paleocurrent directions with reversals. Changes in detrital provenance corresponding to paleocurrent reversals are also recognized. These characteristics are similar to K-T boundary sandstone complexes reported from the Gulf of Mexico region, and strongly support a K-T boundary tsunami origin for the Moncada Formation. The pattern of paleocurrent reversals in the Moncada Formation suggests that tsunami waves were not simple alternations of a single beat, but rather alternations of double beats following the first wave that came from the south. In addition, the maximum grain-size variation within each unit suggests the presence of higher frequency waves superimposed on the lower frequency waves. Thus, our results suggest that K-T impact tsunami waves had a complex rhythm that was caused either by reflections and diffractions of waves or by multiple tsunami waves created by multiple gravity-flows triggered by seismic shocks of the impact.
|ジャーナル||Special Paper of the Geological Society of America|
|出版ステータス||出版済み - 1 1 2002|
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